1. Field of the Invention
The invention relates generally to automatic flight control apparatus having command data selectors which can be set by the pilot in either an incremental or slew mode, and more specifically, the invention relates to a high resolution gear changer for a manually operated multiple speed input data selector apparatus.
2. Description of the Prior Art
Modern commercial and military aircraft are generally equipped with automatic flight guidance control systems and flight guidance indicators which include command data selectors or transmitters which permit the pilot to manually select guidance data. In many cases these settings may be directly inputted to the control system in either an incremental or slew mode. For example, in a typical autopilot course select control, the data tranmitters include a course select synchro and a course select resolver. A typical course select synchro is disclosed in U.S. Pat. No. 2,732,550 for manually setting the course select pointer of a typical radio direction-indicating instrument. Another typical horizontal situation indicator is disclosed in U.S. Pat. No. 3,631,476, wherein the course select pointer is set from a remote selector thereby generating a course reference for an autopilot and/or flight director. The above U.S. Pat. No. 2,732,550 also discloses a course select resolver also positioned by the course selector for establishing the course reference for a VOR receiver. The course select synchro and the course select resolver, therefore, transmit data essential for setting a radio defined course for the aircraft and are conventional components in modern autopilots and flight display instruments. For convenient and efficient operation it is desirable, that the pilot be able to manually set simultaneously both the course select synchro and the course resolver in an incremental fashion for making small course changes and in a slew fashion for making larger changes.
Prior art attempts to provide the pilot with an apparatus that operates in an incremental and slew mode for setting both the course select synchro and the course select resolver have utilized gear shifting devices. These gear shifting devices are of a type having two driving gears mounted on a slidable and rotatable shaft that is spring loaded for maintaining the shaft in either a fine or coarse adjustment mode, i.e., an incremental or slew mode. Ordinarily, the shaft is disposed in a coarse adjustment mode wherein the first driving gear having a relatively large diameter engages a relatively small driven gear mounted on a second shaft. Thus, a rotation of the first shaft produces a relatively large rotation of the second shaft. When an axial force is applied to the first shaft, the first shaft is displaced inwardly disengaging the first relatively large driving gear from the relatively small driven gear. This inward displacement causes the second relatively small driving gear mounted on the first shaft to engage a second relatively large driven gear mounted on a third shaft. Thus a rotation of the first shaft in the fine adjustment mode produces a relatively small rotation of the third shaft. The rotation from the second and third shaft is coupled to the course select synchro and the course selected resolver in a manner well known in the art, thereby allowing both the synchro and the resolver to be set in either an incremental or a slew mode at the operator's discretion.
When utilizing the aforementioned prior art gear shifting technique to set the resolver and the synchro, undesired transients or glitches will occur if the gear teeth are not precisely aligned when the select knob is pressed or released. It is highly desirable that no sensor (synchro or resolver) movement occurs when changing from an incremental to slew mode or vice versa. Any gear movement is multiplied by the gear ratio difference at the sensor. This gear ratio difference is typically on the order of ten to one. Thus, changing from a fine adjustment mode to a course adjustment mode or vice versa will magnify these undesired effects. Since these devices, i.e., the course select synchro and the course select resolver ultimately control the aircraft through the autopilot, it is highly desirable to eliminate these transients or glitches altogether, otherwise the modern autopilot is so sensitive that it will respond to them. Therefore, there is a need to provide modern flight controls with a solution to the problems associated with conventionally changing the selector apparatus between an incremental mode and a slew mode such that smooth operation of the automatic flight control system may be provided during mode changes.
Another disadvantage of the prior art speed change mechanism, and one which is particularly annoying to the pilot, is the probability that when the selector knob is pressed, the gear teeth will not be properly aligned. The gear teeth may actually abut and prevent further knob movement and gear engagement, thus requiring the pilot to rotate the knob slightly in order to effect gear engagement. This problem has been reduced somewhat by shaping or tapering the tooth edges, but this is a very tedious, time consuming and hence very expensive technique. This technique, however, further aggravates the gear mesh transients discussed above.